Hydraulic Control Assembly - Antilock Brakes: Service and Repair

Hydraulic unit, replacing

Preparation

Disconnect the battery lead
See Battery, disconnecting Battery Disconnecting.

Warning! Never, under any circumstances, open the ABS hydraulic modulator. Reassembling it requires special equipment and facilities.

Note! An ABS modulator for ABS has only eight valves while an ABS modulator for ABS and STC (stability and traction control) has ten valves. The method for replacing the unit is the same for both types. Check thoroughly when installing the new unit that the unit is the correct type.

Removal

Preparations




Switch off the ignition
Place paper under the ABS hydraulic modulator as protection against brake fluid spillage.
Depress the brake pedal a few times so that no vacuum remains in the servo unit.
Clean the brake pipes terminals at the ABS hydraulic modulator and master cylinder

Depressurize the brake system




Secure the pedal in the depressed position. Use a pedal jack.
Remove the protective cap from the bleed nipple at the left front wheel.
Install a plastic hose on the nipple.
Open the bleed nipple.
Collect the brake fluid in a container (bottle).
Shut the bleed nipple.

Preparations for removal of the ABS hydraulic modulator

Remove plastic cap and positive cable nut
See Brake pipe master cylinder / ABS unit, replacing Brake Pipe Master Cylinder / ABS Unit, Replacing.

Remove the integrated relay / fusebox. Remove the connector for the ABS unit
See Replacing the brake pipe between the hydraulic unit, front wheel and junction Brake Pipe Hydraulic Unit / Junction / Front Wheel, Replacing.

Remove the air cleaner (ACL) housing
See Brake pipe master cylinder / ABS unit, replacing Brake Pipe Master Cylinder / ABS Unit, Replacing.

Remove the brake pipes between the master cylinder and the ABS unit
See Brake pipe master cylinder / ABS unit, replacing Brake Pipe Master Cylinder / ABS Unit, Replacing.

Remove the ABS hydraulic modulator with its bracket




Disconnect the brake pipes to the wheel brakes from the ABS hydraulic modulator.
Hang the brake pipes on the cross member.
Plug the brake pipes and connections for the ABS hydraulic modulator and master cylinder. This is to prevent contaminants entering the system.
Remove the 3 mounting screws for the bracket by the side member. Lift up the bracket.

Remove the ABS hydraulic modulator from the bracket





Note! The ABS hydraulic modulator must be replaced as a complete unit.

Remove:
- the connector for the pump motor from the control module
- the bracket from the ABS hydraulic modulator
- the control module.

Checking the ABS hydraulic modulator




Check that the new ABS hydraulic modulator is the correct type depending on whether the car is equipped with STC (stability and traction control) or not.
An ABS modulator for ABS has only eightvalves while an ABS modulator for ABS and STC (stability and traction control) has ten valves.

Warning! Never, under any circumstances, open the ABS hydraulic modulator. Reassembling it requires special equipment and facilities.

Installation

Check the control module
Model years -2001.
See Control module (ABS), replacing .
Model years 2002-.
See Brake control module (BCM), replacing Brake Control Module (BCM), Replacing.

Assemble the ABS hydraulic modulator and the bracket





Note! The ABS hydraulic modulator is filled with brake fluid. It is important that the plugs are not removed until the brake pipes are to be connected.

Install the new ABS hydraulic modulator
Install the new ABS hydraulic modulator on the bracket. Tighten the mounting screws. Tighten to 8 Nm.
Hold the vacuum hose to one side and carefully install the bracket in the car (the hose between the bracket and the side member).
Connect the pump motor connector to the control module. Tighten the mounting screws. Tighten to 8 Nm.

Installing the ABS hydraulic modulator, continued




Remove the protective plugs. Connect the brake pipes to the ABS hydraulic modulator and the master cylinder. Tighten to 14 Nm.

Install the integrated relay / fusebox and ABS unit connector





Install:
- the connector for the ABS control module
- the screw for the bracket for the integrated relay / fuse box.

Finishing work

Warning! No ABS, stability and traction control functions are available when there is communication with the Brake control module (BCM) (Volvo Diagnostics are activated). ABS warning lamp flashes for as long as the diagnostics are activated. To cancel the diagnostics before test driving the vehicle, the ignition must be switched off!

Remove the pedal jack.

Bleed the brake system
See Brake system, bleeding (using bleeding unit) Brake System, Bleeding (Using Bleeding Unit).
Wash off any spilled brake fluid. Use warm water and car shampoo.

Function test
See Wheel sensor, front, replacing Wheel Sensor, Front, Replacing.